The present invention relates to motor vehicle crash discrimination systems utilized for actuating or deploying a passenger safety restraint, and more specifically to a system and a method for actuating a passenger safety restraint which utilizes detected occupant position to achieve improved functionality and reliability.
Conventional vehicle crash discrimination systems typically employ at least one acceleration sensor affixed to the vehicle for sensing vehicle acceleration. The sensor's output is supplied to a crash discrimination circuit which determines at least one crash measure, such as a value for vehicle velocity through integration of the sensor's output over time, for subsequent comparison to a predetermined threshold value. If the predetermined threshold value is exceeded, the discrimination circuit outputs a trigger signal which actuates or deploys a passenger safety restraint, such as an air bag or passive seat belt pretensioning mechanism.
The time at which such an accelerometer-based crash discrimination circuit actually generates this trigger signal, relative to the beginning of the crash, is known as the "actual time to fire;" and a given accelerometer-based crash discrimination circuit inherently provides a range of such actual times to fire, as generally determined by the profile of the crash experienced by the vehicle (sometimes referred to as "crash type"). Specifically, in the above example, since the relative amount of time required in order for the velocity value (integrated acceleration) to exceed the threshold value necessarily depends upon the individual values for acceleration data generated by the sensor, and since a severe crash type is likely to generate higher individual acceleration values than those generated by a moderate crash type, a given accelerometer-based crash discrimination circuit is inherently capable of generating the trigger signal over a range of times relative to the beginning of the crash.
One failing of such conventional accelerometer-based crash discrimination systems is that they fail to account for variations in vehicle passenger/occupant conditions (whether static or dynamic) in determining whether to actuate the safety restraint, particularly as these variations affect the amount of time otherwise available for crash discrimination while still permitting safe and complete actuation/deployment of the safety restraint. This maximum amount of time for crash discrimination analysis, as measured from the beginning of a crash, is the "required time to fire" of the safety restraint. More specifically, conventional accelerometer-based crash discrimination systems are generally designed to assume a set of "nominal" occupant conditions, such as the presence within the vehicle of a 50th-percentile male occupant and the failure of such an occupant to wear a seat belt, as well as a fixed required time to fire.
The use of these assumed "nominal" conditions by known crash discrimination systems tends to ensure proper actuation of the safety restraint only to the extent that they accurately describe the actual occupant conditions at the time at which severe vehicle acceleration (deceleration) is detected by the accelerometer. Correlatively, the use of this single set of assumptions, with its attendant required time to fire, inherently causes unnecessary, ill-timed, or perhaps even undesired actuation of the safety restraint where the assumed conditions are not otherwise met by the occupant at the time the accelerometer indicates severe vehicle acceleration, as when there is no occupant present within the vehicle; or when the occupant is not a 50th-percentile male; or in marginal crash situations where a seat belt otherwise provides sufficient safety protection for the occupant; or in crash situations where the occupant is improperly positioned relative to the safety restraint such that actuation of the safety restraint could itself injure the occupant. Moreover, where the vehicle occupant to be protected is a front-seat passenger rather than the vehicle's driver, many additional occupant condition scenarios are raised, such as that of a child moving around in the seat at the start of a crash; or a child moving into the front passenger seat from a rear seat as a crash begins; or a rear-facing infant seat positioned only a few inches away from the point of deployment of the safety restraint; or an adult bending over to pick something up off the vehicle floor as a crash begins; or a passenger holding a heavy object near the deployment point; or a parent holding a child on her lap. Finally, to the extent that actual occupant conditions indicate a longer required time to fire, such prior art crash discrimination systems fail to utilize that additional time for increased decisional reliability, let alone the additional acceleration information generated during that additional time.
Another known vehicle crash discrimination system disclosed in U.S. Pat. No. 5,118,134 to Mattes et al utilizes both sensed vehicle acceleration and the occupant's transitory displacement from a nominal seating position in determining whether to actuate a safety restraint. A further embodiment uses sensed transitory occupant velocity, as measured by the relative change in detected occupant displacement over time, as a third trigger criterion. The relative occupant displacement and/or transitory occupant velocity is measured using ultrasonic, light or microwave signals as transmitted between fixed transmitters and receivers mounted either longitudinally or transversely of the vehicle, with the latter configuration providing an indication of occupant displacement from his nominal position as he "breaks" each one of several planes defined by the transducers within the passenger compartment. In the preferred embodiment, the system compares the present-sensed vehicle acceleration to a first threshold value, the relative displacement of the occupant from his nominal position to a second threshold value, and the relative velocity of the occupant to a third threshold value. The safety restraint is actuated when the first threshold value and either one of the second or third threshold values are simultaneously exceeded.
While the system disclosed in U.S. Pat. No. 5,118,134 to Mattes et al improves reliability over conventional accelerometer-based crash discrimination system through its use of displacement of an occupant from his nominal position and, perhaps, of transitory occupant velocity information derived from such occupant displacement, the system remains relatively rigid due to its reliance upon but a single set of decisional criteria (the predetermined threshold values for vehicle acceleration, occupant displacement from nominal and transitory occupant velocity), as well as the use in the preferred disclosed embodiment of relatively low-resolution, noncontinuous occupant position information obtained with the primary "break-the-plane" transducer configuration. Stated another way, while the arrangement of Mattes et al attempts to accommodate gross displacement of the occupant from his nominal seating position by making such displacement an additional trigger criterion, the system does not otherwise accommodate various deviations from assumed nominal conditions, including volitional occupant movement, which affect the manner in which other trigger criteria are best utilized for crash discrimination analysis.